They are described by hundreds of witnesses as grey-skinned beings: no ears, no nose and bulbous black eyes. Are these so called "Greys" visitors from another planet? The team investigates stories of abductions in two different countries--their harrowing accounts disturbingly similar. In hypnotic regression, eyewitnesses describe being taken aboard alien spacecraft as part of a bizarre program to form "hybrid" beings. The team tracks down potential proof: an unusual, one-of-a-kind skull discovered in a cave in Mexico that bears an eerie resemblance to the Greys described by abductees.